The present invention relates to a luminescent diode formed from a mixed crystal epitaxial layer comprising a composition A.sub.1-x.sup.III Al.sub.x B.sup.V with a substantially continuously varying value x. A pn-junction is present in the layer formed between n and p-doped layer components.
For more than half a decade there have been luminescent diodes consisting of gallium-aluminum-arsenide in whose mixed crystal-epitaxial layer the layer-wise local concentration of the aluminum fraction, which replaces a corresponding gallium fraction, is variable with a constant gradient. Such a construction of the mixed crystal layer is designated in the art as a "graded-bandgap". Such an arrangement has a bandgap which is constantly greatly varying, corresponding to the constantly changing aluminum concentration, and has the greatest bandgap with the maximum aluminum concentration. The purpose of such a mixed crystal is to be able to allow recombination-luminescence radiation produced in a layered region with at least a virtually constant aluminum concentration to emerge from the entire mixed crystal-layer in such fashion that this radiation penetrates regions of the layer in which (on account of greater aluminum concentration there) the bandgap is greater. Thus, reabsorption of the produced luminescence radiation is prevented to this extent.
The pn-junction contained in the mixed crystal-layer of a luminescent diode with a "graded-bandgap", whose surface extends perpendicularly to the vector of the gradient of the aluminum concentration, is, in the case of these already long-known luminescent diodes, produced by means of silicon doping. The silicon has an amphoteric doping behavior in such a mixed crystal, specifically if it is dependent upon the deposition temperature.
Further details of such a known diode can be learned from "Siemens Research and Development Reports', Vol. 9 (1980), No. 6, pp. 339-346. In this state of the art publication, not only is such a known luminescent diode described, but also the pertinent method steps for manufacture, the properties of such a diode, and also its preferred application are described in detail. The contents of this publication are incorporated by reference herein.
Luminescent diodes with a "graded-bandgap" have a relatively large half-intensity width of their emission-spectrum.
In addition to the luminescent diodes of the above-described type, there are additional types of luminescent diodes. Thus, for example, luminescent diodes having a single heterostructure and having a double heterostructure are known. Such diodes containing at least two epitaxial layers are manufactured in two separate epitaxial steps.